PROJECT DESCRIPTION / SUMMARY Much of our collective knowledge on vascular growth has emerged from efforts to understand angiogenesis, a process by which endothelial cells depart from pre-existent vessels to form new vascular beds. Nonetheless, once formed, vascular tubes also expand in width, length, and are able to regenerate. Regeneration is extremely important to the repair of endothelial damage imposed by stents and other medical devises, as well as to mediate heal after physical/chemical trauma. However our understanding of the cellular and molecular mechanisms that regulate endothelial growth and regeneration within the context of a fully functional, blood perfused and pulsatile vessel are limited. Our preliminary data show that expansion of the tunica intima in vivo occurs through intrinsic proliferation of intimal endothelial cells in a polarized and organized manner. In fact, a subset of endothelial cells flanking a wound are robustly induced to enter into the cell cycle as quickly as 12 hours following injury in a highly synchronized fashion. The process is initiated by changes in cell-cell junctions that trigger molecular rewiring and impressive physiological changes. Important outcomes of these responses include alterations in endothelial cell polarity, induction of chromatin remodeling, adjustments in metabolism and a quick emergence of a transcriptional signature that is unique to regenerative endothelium. This newly identified signature is finely tuned by the timed release of stress signals that appear to act differentially in the subsets of endothelial cells, revealing an intrinsic heterogeneity that controls the threshold for regeneration in a given vessel. In fact, genetic tracing analysis using endothelial-specific rainbow mice revealed the presence of cells with different proliferative potential suggesting the intercalation of progenitors within the wall of the endothelial monolayer. Taken together, these studies are paradigm shifting for understanding the mechanisms controlling endothelial regeneration and their deregulations in settings like chronic/acute inflammation, aging, chronic diseases and physical trauma. Through this NHLBI Outstanding Investigator Award application our goals are to (1) decode the cellular and molecular mechanisms controlling the process of endothelial expansion within a formed vessel; (2) clarify the process involved in endothelial regeneration and repair: (3) understand how hijacking these mechanisms might either accelerate or impair endothelial regeneration; (4) identify novel targets for therapeutic interventions aimed at endothelial repair during stenting or other injuries. These series of broadly defined aims have been conceptualize to fill gaps of our knowledge on fundamental biological processes in endothelial cell biology but also to exploit this information for application during medical interventions such as stent coverage. We are energized by the opportunity afforded by this grant mechanism and for the potential translational impact of these studies.